This invention relates to an improved process for phosphate beneficiation. In particular, this invention relates to the use of a high molecular weight polyethylene polyamine condensed with a fatty acid, fatty acid ester or with a fatty acid and an alkylolamine in the flotation of siliceous material from phosphate.
In the present commercial beneficiation of siliceous phosphate ores, a deslimed and sized phosphate ore is conditioned with and then floated by a fatty acid collector and fuel oil reagent in an aerated aqueous solution at a pH of at least about 8. This flotation process produces a low-grade phosphate concentrate containing from about 50 to 65 weight percent bone phosphate of lime (BPL). The "rougher float concentrate" from the aforementioned flotation is blunged with acid to remove fatty acid collector coatings and the phosphate is further concentrated by flotation of residual silica from the concentrate with a so-called cationic amine collector.
U.S. Pat. No. 2,278,060 teaches that the reaction product of a polyalkylene polyamine with a fatty acid, a fatty acid glyceride or other fatty acid esters, as well as their corresponding water-soluble salts, can be used as cationic amine collectors. U.S. Pat. No. 2,278,107; 2,312,387; 2,322,201; and 2,710,856 also disclose the use of reaction products of a polyalkylene polyamine with a fatty acid, alone or in combination with other flotation agents, to effect the flotation of silica from phosphate. However, the above-identified references explicitly disclose polyethylene polyamines having only 8 or fewer carbon atoms in the reaction with the fatty acid. The polyethylene polyamines having a molecular weight less than 200 grams per mole, in particular diethylenetriamine, condensed with a fatty acid are currently the cationic amine collectors of choice.
The above-described cationic amine collectors are effective in the recovery of BPL from phosphate ore, but the condensates of lower molecular weight polyethylene polyamines suffer from a number of deficiencies. U.S. Pat. No. 3,640,862 discloses that these cationic amine collectors are viscous pastes which are difficult to disperse in water. Further, the effectiveness of these collectors is severely diminished in the presence of residual fatty acid collector coatings from a first flotation step. Residual fatty acid, present in as litte as 0.01 kilogram per ton of feed, has an adverse impact on the selectivity of the prior art collector. U.S. Pat. No. 2,710,856 teaches that unsubstituted polyalkylene polyamines react incompletely with the rosin acids contained in tall oil, which results in an amine collector of inferior selectivity. Finally, the demand for diethylenetriamine in alternative, less cost-sensitive uses has resulted in a steady escalation in the price of diethylenetriamine. This increasing price has spurred a search in the phosphate industry for a flotation agent possessing greater cost-effectiveness, which does not possess the deficiencies of the prior art collectors.